In large refrigeration systems it is the practice to defrost the refrigeration coils regurlarly to remove the ice formed thereon by condensation of water from the ambient atmosphere, since ice on the coils act as a heat insulator to reduce the efficiency of the system. During defrosting water and pieces of ice drop from the refrigeration coils, and it is preferred practice to position a defrost pan beneath the coils to receive the water and discharge it appropriately. Since such pans are customarily in position continuously, they become cold during the refrigeration cycle so that material falling on them would ordinarily freeze there rather than discharge as a liquid, the custom has developed of supplying heat to the pans at the same time of defrosting. This is usually done by circulating hot gas from the refrigeration compressor through conduits in heat conductive relation to the pan, with the intent that the pans will become warm enough, in the interval during which the coils themselves are being warmed, to avoid freezing the falling material.
The pan conduits have heretofore been patterns of tubing engaging the outer surface, or the inner surface, of the steel pan. With this arrangement, it is very difficult to achieve sufficent heat conductivity between the round tubing and the flat pan to enable adequate heat transfer to the pan within the constraints of time and available heat.
It is also known to form the pan material itself to furnish passages for hot gas lobe between two sections of steel welded together, one section forming the bottom of the pan itself. This arrangement is commonly referred to as a "waffle pan" construction, and is also quite expensive to manufacture.